Research Trends in the Economic Analysis of Municipal Solid Waste Management Systems: A Bibliometric Analysis from 1980 to 2019

: This article analyzes state-of the art studies that focus on the economic aspects (EA) of municipal solid waste (MSW) management systems, including an analysis of articles that have developed methodologies for economic analysis (MEA), as well as those which study the economic analysis of the externalities or external impacts related to these systems. The aim of this study was to determine the trends in research and critical points based on the literature available in the Web of Science database from 1980 to 2019. First, we present the statistics and general trends, then perform an in-depth bibliometric study using the VOSviewer software, which allows the results to be grouped according to references, authors, institutions, countries, and journals. The study showed that 563 articles about the economic aspects have been published, 229 about methodology development, and only 21 considered the methodologies for analyzing externalities generated by the MSW management systems. In general, there is great interest in the economic analysis of the systems and technologies that deal with transforming waste into energy.


Introduction
Currently, countries face a serious problem due to the generation and management of greater quantities of waste caused by economic growth and new economic models based on encouraging ever-greater consumption rates in society [1,2]. The large-scale production of waste has led to the development of several operations (i.e., collection, transport, treatment, and elimination) for its management [3]. Specifically, when waste management is centered on the management of domestic waste, or waste of similar characteristics, it is known as municipal solid waste (MSW) management. Depending on the city or country, the complexities and characteristics of these operations may vary; for example, in developed countries, the processes and systems are more complex and use more sophisticated technologies and infrastructures. On the other hand, in developing countries, the processes are generally simpler and the informal waste sector has a notable presence [4,5].
When an MSW management system is implemented it can generate different impacts or consequences, which may be reflected as revenues or costs depending on whether the parties involved are affected positively or negatively. A distinction is usually made between internal and external impacts. In general, the economic-financial analysis of MSW management systems focusses only on studying the internal or private impacts, costs, and revenues related to OPEX (operational which one specific item appears next to another. The thickest lines of the links show a more regular co-occurrence, in other words, greater intensity of cooperation [23,26]. This co-occurrence between nodes is also reflected in the distance between them. The color of the elements represents a group of items connected by their affinity to the subjects of research, elements of the same color being known as clusters [26]. studied the economic aspects of MSW system management; a total of 563 results were obtained and identified as economic aspects (EA). The second search added other terms to those of the first, such as Topic: (Methodology OR Model) to determine which articles had developed or presented a method or model for the economic analysis of MSW management systems. It obtained 229 results, in this case classified as methodologies for economic analysis (MEA). Finally, the third search added further limits to those of the first and second, such as Topic: (Externality OR External Cost) to determine which articles developed or presented a methodology to evaluate economically the externalities related to the MSW management systems, obtaining only 21 results. The complete register (composed mainly of the authors, titles, sources, and abstracts of the publications), as well as the references quoted, were downloaded in txt format for mapping and network analysis. In Figure 1, the methodology used to search and obtain data and data treatment is presented.

Results
First, we present the general trends in research, which includes the number of publications per year, the number of citations per field and document, the countries with the most publications, and the most representative authors [23]. Then, we analyzed the current situation and the development of research into the economic aspects (EA) of the MSW management systems, which consisted of 563 articles; in addition, we provided information about the articles that contain methodologies for the economic analysis (MEA) of MSW management systems, which consisted of 229 articles. The second part of this section concentrates on the most cited documents regarding the economic analysis of MSW management systems (referring to the themes of EA and MEA). The third analyzes the most representative journals in the field. Next, we give information about the articles that have developed methods for the economic analysis of the external impacts or externalities (this search contained only 21 articles). The fifth part studies the analysis of the coincidence of authors' keywords regarding the economic analysis (EA) of the MSW management systems. Then the article explores the co-citation of references, journals, and authors on the subject of EA. Finally, we studied the co-authorship networks of countries and institutions involved in the research of EA.

General Trends
The first document about EA appeared in the WoS in 1980. From this year onward there was an intermittent flow of documents, which were not published every year. However, after 1988, documents appeared every year, staring with 1 article in 1988 and rising to 75 in 2019. The annual publications about the economic aspects of MSW management systems are shown in Figure 2, where it can be seen that interest in the research of the subject has grown. Although the search for the economic aspects of the MSW systems only generated 563 results, calculating the increase in the last 10 years (2010 to 2019) shows a rise of more than 294.74%. and 7.81% of all publications on the subject. In addition, 80 countries have contributed to the development of the 563 publications. In the case of MEA, the countries with most publications are the USA with 31, Italy with 26, and China with 19. These represent, respectively, 13.53%, 11.35%, and 8.29% of all publications on the subject. It should be noted that the developed countries are to be found among the most representative, which reflects the developing countries' lack of interest in research into the economic aspects of MSW management.  In the case of the documents relating to MEA, the first article appeared in 1991, since when there has been an intermittent generation of articles. However, after 2003 more documents appeared every year, starting with 3 in 2003 and reaching a total of 40 in 2019. Although the search for the development of methods for the economic analysis of the MSW systems generated only 229 results, calculating the increase of the last 10 years shows that there has been a rise of more than 471.43%.
As can be seen in Figure 3, the countries with most publications dealing with EA are the USA with 87 publications, Italy with 59, and China with 44. These represent, respectively, 15.45%, 10.48%, and 7.81% of all publications on the subject. In addition, 80 countries have contributed to the development of the 563 publications. In the case of MEA, the countries with most publications are the USA with 31, Italy with 26, and China with 19. These represent, respectively, 13.53%, 11.35%, and 8.29% of all publications on the subject. It should be noted that the developed countries are to be found among the most representative, which reflects the developing countries' lack of interest in research into the economic aspects of MSW management.
Sustainability 2020, 12, x FOR PEER REVIEW 5 of 20 As can be seen in Figure 3, the countries with most publications dealing with EA are the USA with 87 publications, Italy with 59, and China with 44. These represent, respectively, 15.45%, 10.48%, and 7.81% of all publications on the subject. In addition, 80 countries have contributed to the development of the 563 publications. In the case of MEA, the countries with most publications are the USA with 31, Italy with 26, and China with 19. These represent, respectively, 13.53%, 11.35%, and 8.29% of all publications on the subject. It should be noted that the developed countries are to be found among the most representative, which reflects the developing countries' lack of interest in research into the economic aspects of MSW management.   The influence of the articles can also be measured by analyzing the number of citations. Table 1 shows the level of citations of all the articles published on EA, where it can be seen that only 7.11% (40) of the total (563) have more than 50 citations, 12.43% (70) have between 25 and 49 citations, 22.02% (124) have between 10 and 24 citations, and 58.44% (329) have less than 10 citations. The hindex of the articles about EA is 45 (i.e., 45 articles have at least 45 citations). In the case of articles about MEA, it can be seen that only 6.99% (16) of the total (229) have more than 50 citations, 8.73% (20) have between 25 and 49 citations, 24.89% (57) have between 10 and 24 citations and 59.40% (136) have less than 10 citations. The h-index of the articles related with MEA is 28.    The influence of the articles can also be measured by analyzing the number of citations. Table 1 Table 2 shows the most-cited articles in the fields of EA and MEA, as well as some specific characteristics such as the journals where they were published, the total number of citations (NC), citations per year (CY), and the main results.  Regarding research into EA, 33.33% of the 15 most-cited articles were published in the journal Waste Management ( Table 2) [32] with 114 citations. In both cases, these articles focus mainly on the economic analysis of technology and systems for generating energy from waste, waste collection costs, and the assessment of different recycling systems.  44.10% have been published in the top 10 journals. Research into EA represents just a small percentage of the total amount of research carried out in the top 20 journals (with coverage varying from 0.01% to 1.19%). In the case of MEA, the research carried out in the top 10 journals represents coverage of 0.02% to 0.55%.

Publications Related to Externalities
The search in WoS using the terms "Methodology" or "Model", as well as "Externality" or "External Costs", produced 21 publications, with 23.80% of the articles published in the journal Waste Management. Of all the articles, 23.80% were published before 2010, 38.10% appeared between 2010 and 2015, and 38.10% were published after 2015. Table 4, shows the most-cited articles that considered external costs or benefits, where the most-cited was Massarutto et al. (2011) [44] with 59 citations. This work developed a model based on the principles of life cycle costing (LCC), which includes externalities such as air emissions (from incineration, landfills and collection vehicles), climate change (CO 2 ), and disamenities. Rabl et al. (2008) [45], with 55 citations, presented a methodology for evaluating external costs due to pollution from waste treatment is described, based on the ExternE project series of the European Commission. In this case, energy, material recovery, and possible differences in transport distance are considered. Martinez-Sanchez et al. (2015) [9] presented a costs model for the economic valuation of MSW management systems, had 40 citations. This model was based on the principles of LCC and considered the following external costs: environmental emissions and society's willingness to pay to prevent emissions or impacts of the MSW systems.
It must be pointed out that there are some articles that show an extensive review of the principal external impacts generated by MSW management systems [12,46]. They provide a general view of the external costs or externalities associated with several MSW management systems, such as disposal in a landfill and waste incineration, including different valuation methods. These articles are not included in the 21 obtained results because they do not provide methods for the economic valuation of the externalities that would allow them to be identified and their monetary value assessed.

Keyword Analysis
The keywords generally indicate the main content and subject of the article's research, showing trends in research and the most important subjects in a specific area [23]. "When working with keywords, the occurrences attribute indicates the number of documents in which a keyword occurs" [26] (p. 36).
Examining the 563 articles about researching the EA of MSW management systems, the analysis reveals the existence of 1493 keywords. Figure 5 shows the principal keywords, organized in 9 clusters, where the most frequent keywords per cluster are as follows: recycling, circular economy (red cluster); MSW, costs (green cluster); MSW, renewable energy (dark blue cluster); biogas, economic analysis (yellow cluster); anaerobic digestion, gasification (purple cluster); MSW, techno-economic analysis (light blue cluster); waste management, waste-to-energy (orange cluster); life cycle assessment, incineration (brown cluster); and landfill, leachate (pink cluster). clusters, where the most frequent keywords per cluster are as follows: recycling, circular economy (red cluster); MSW, costs (green cluster); MSW, renewable energy (dark blue cluster); biogas, economic analysis (yellow cluster); anaerobic digestion, gasification (purple cluster); MSW, technoeconomic analysis (light blue cluster); waste management, waste-to-energy (orange cluster); life cycle assessment, incineration (brown cluster); and landfill, leachate (pink cluster).
It can be seen that among the top 20 keywords some, related to the transformation of waste into energy, stand out, such as incineration, waste to energy, renewable energy, and biogas. It can also be seen that the most common methods for the economic assessment of MSW systems are the life cycle costing and cost-benefit analysis.
There are also keywords related to some specific types of waste, such as "food waste" and "organic waste"; the importance of the research into these is due to the fact that they are the world's most widely-generated waste types [1,53]. The presence of the keyword "packaging waste" is also noticeable, its importance lying in the several negative impacts (environmental and economic) that can arise if it is not managed adequately, as in the case of "plastic packaging waste" [54,55]. The research and design of viable economic, social, and environmental technologies and MSW systems is essential, as is the development of techniques to improve the management and reduce generation of these wastes, which would lead to a reduction in possible negative impacts.  It can be seen that among the top 20 keywords some, related to the transformation of waste into energy, stand out, such as incineration, waste to energy, renewable energy, and biogas. It can also be seen that the most common methods for the economic assessment of MSW systems are the life cycle costing and cost-benefit analysis.
There are also keywords related to some specific types of waste, such as "food waste" and "organic waste"; the importance of the research into these is due to the fact that they are the world's most widely-generated waste types [1,53]. The presence of the keyword "packaging waste" is also noticeable, its importance lying in the several negative impacts (environmental and economic) that can arise if it is not managed adequately, as in the case of "plastic packaging waste" [54,55]. The research and design of viable economic, social, and environmental technologies and MSW systems is essential, as is the development of techniques to improve the management and reduce generation of these wastes, which would lead to a reduction in possible negative impacts. Table 5 shows the top 20 keywords, as well as the occurrences (frequency) and co-occurrences link (total strength of link). Regarding occurrence, the most important keywords are municipal solid waste, biogas, and waste management; in the case of the co-occurrence link, the most important keywords are municipal solid waste, waste management, and recycling.

Reference, Journal, and Author Co-Citation Analysis
This section analyzed co-citation (cited references, cited sources, and cited authors). Co-citation is defined as the frequency with which documents are cited together; when a third item cites two elements (author, reference, or journal) there is a co-citing relationship [56]. A co-citation link is a link between two elements cited by the same document, in this case the distance between two journals, authors or references shows the relationship of these items in terms of citation links. In general, the closer the nodes the stronger their relationship. The strongest co-citation links between nodes are also represented by lines [26].
First, an analysis was performed on the co-citation of cited references ( Figure 6), obtaining three clusters where the most representative articles of each cluster are as follows. Leme et al. (2014) [31] (in red) with 24 citations and a total link strength of 52 (in first place for citations). This work compares different alternatives for generating energy from MSW in Brazil, from a techno-economic and environmental perspective. This cluster also included   [27], Jamasb and Nepal (2010) [57], and others. Its main focus is the analysis of systems that transform waste to energy.  Regarding the analysis of the journal co-citation network, there are 3 clusters (Figure 7). The green cluster includes Waste Management, the journal with most citations (1557) and the highest link strength (24215). This cluster is composed of journals on subjects related to environmental and sustainability issues, and specifically dealing with waste management (generation, characteristics,  [40] (in green) have 10 citations and a total link strength of 43, developing a model to examine the costs, employment, and recovery rates achieved using various waste recovery methods including recycling and incineration. This cluster also included: Reich (2005) [30]; Eshet et al. (2006) [46], among others. Its main focus is the analysis and comparison of different MSW management systems. Dijkgraaf et al. (2003) [58] (in blue) have 15 citations and a total link strength of 85 (in first place for total link strength); this work focusses on collection systems in the Netherlands. It can be seen that the blue cluster is further away from the other two clusters, which shows a weaker relationship between the subjects under research. This cluster also included Callan and Thomas (2001) [35], Bel and Warner (2008) [59], and others. Its main focus is the cost analysis of MSW collection services.
Regarding the analysis of the journal co-citation network, there are 3 clusters (Figure 7). The green cluster includes Waste Management, the journal with most citations (1557) and the highest link strength (24215). This cluster is composed of journals on subjects related to environmental and sustainability issues, and specifically dealing with waste management (generation, characteristics, reduction, collection, separation, treatment, and elimination). The most representative journal of the red cluster (the most numerous) is Bioresource Technology (Citations: 440, Link Strength: 9665); this cluster is mostly made up of journals dealing with subjects such as energy and its generation, conversion, and use. Finally, the most representative journal of the blue cluster is the Journal of Cleaner Production (Citations: 492, Link Strength: 10108); this cluster contains interdisciplinary journals focusing on research into the environment and sustainability, as well as the use of resources, water, and energy. In this case, it can be seen that two of the clusters (blue and green) are closely linked, which shows that their subjects of research (waste management, environmental issues, and sustainability) are closer, whereas the red cluster is composed of journals whose principal subjects of research are connected with the generation of energy from waste. between the subjects under research. This cluster also included Callan and Thomas (2001) [35], Bel and Warner (2008) [59], and others. Its main focus is the cost analysis of MSW collection services. Regarding the analysis of the journal co-citation network, there are 3 clusters (Figure 7). The green cluster includes Waste Management, the journal with most citations (1557) and the highest link strength (24215). This cluster is composed of journals on subjects related to environmental and sustainability issues, and specifically dealing with waste management (generation, characteristics, reduction, collection, separation, treatment, and elimination). The most representative journal of the red cluster (the most numerous) is Bioresource Technology (Citations: 440, Link Strength: 9665); this cluster is mostly made up of journals dealing with subjects such as energy and its generation, conversion, and use. Finally, the most representative journal of the blue cluster is the Journal of Cleaner Production (Citations: 492, Link Strength: 10108); this cluster contains interdisciplinary journals focusing on research into the environment and sustainability, as well as the use of resources, water, and energy. In this case, it can be seen that two of the clusters (blue and green) are closely linked, which shows that their subjects of research (waste management, environmental issues, and sustainability) are closer, whereas the red cluster is composed of journals whose principal subjects of research are connected with the generation of energy from waste.

Bibliographic Coupling of Authors
The bibliographic coupling of authors analysis allowed us to see if authors A and B cite the articles of author C; in other words, two authors with common references are more closely related and have similar research interests [60].
The bibliographic coupling of authors ( Figure 9) showed that there were eight clusters composed of 35 authors. Red is the main cluster, with 9 authors, the most representative being De Jaeger, S. Then, the green and dark blue clusters had 6 authors each, yellow had 5 authors, purple had 3, and light blue, brown, and orange clusters had 2 authors each.
The authors with most publications are as follows. De Jaeger, S.

Bibliographic Coupling of Authors
The bibliographic coupling of authors analysis allowed us to see if authors A and B cite the articles of author C; in other words, two authors with common references are more closely related and have similar research interests [60].
The bibliographic coupling of authors ( Figure 9) showed that there were eight clusters composed of 35 authors. Red is the main cluster, with 9 authors, the most representative being De Jaeger, S. Then, the green and dark blue clusters had 6 authors each, yellow had 5 authors, purple had 3, and light blue, brown, and orange clusters had 2 authors each. Two clusters can be seen (light blue and brown) further away from the others, which represent recent subjects of research. On the one hand, the cluster formed by authors Ayalon, O. and Shechter, M., whose publications deal with themes regarding the economic valuation of the externalities of the MSW management systems. On the other hand, the cluster composed of Dennison, G.J. and Dodd, V.A., whose works on evaluating the costs of waste recycling focus on Dublin, Ireland.

Country and University Co-Author Analysis
Finally, co-authorship between cities and universities was analyzed, where item size (nodes) reflects the relevance of the organizations or countries, and the distance reflects the degree of collaboration between them. Two clusters can be seen (light blue and brown) further away from the others, which represent recent subjects of research. On the one hand, the cluster formed by authors Ayalon, O. and Shechter, M., whose publications deal with themes regarding the economic valuation of the externalities of the MSW management systems. On the other hand, the cluster composed of Dennison, G.J. and Dodd, V.A., whose works on evaluating the costs of waste recycling focus on Dublin, Ireland.

Country and University Co-Author Analysis
Finally, co-authorship between cities and universities was analyzed, where item size (nodes) reflects the relevance of the organizations or countries, and the distance reflects the degree of collaboration between them.
Analyzing the co-authorship relationships between countries provides us with a network composed of 19 countries spread over 5 clusters (Figure 10 recent subjects of research. On the one hand, the cluster formed by authors Ayalon, O. and Shechter, M., whose publications deal with themes regarding the economic valuation of the externalities of the MSW management systems. On the other hand, the cluster composed of Dennison, G.J. and Dodd, V.A., whose works on evaluating the costs of waste recycling focus on Dublin, Ireland.

Country and University Co-Author Analysis
Finally, co-authorship between cities and universities was analyzed, where item size (nodes) reflects the relevance of the organizations or countries, and the distance reflects the degree of collaboration between them.
Analyzing the co-authorship relationships between countries provides us with a network composed of 19 countries spread over 5 clusters (Figure 10   Finally, from the institutions' co-authorship network (Figure 11) of universities or institutions that meet the threshold of at least 2 documents published, it can be seen that there is little collaboration between different universities. This is due to the fact that, of the 700 universities mentioned, the largest group is only 9, organized into three clusters as follows. collaboration between different universities. This is due to the fact that, of the 700 universities mentioned, the largest group is only 9, organized into three clusters as follows. The red cluster, composed of 4 universities: the IVL Swedish Environmental Research Institute, Sweden (2 documents, 34 citations), Chalmers, Sweden (2 documents, 66 citations), University of Gävle, Sweden (2 documents, 40 citations), and the KTH Royal Institute of Technology, Sweden (2 documents, 20 citations). The green cluster consists of 3 universities: University of Borås, Sweden (5 documents, 130 citations), Chalmers University of Technology, Sweden (3 documents, 50 citations), and RAM Lose Edb, Denmark (2 documents, 27 citations). The blue cluster has 2 universities: Technical University of Denmark (8 documents, 182 citations) and the Fundación ENT, Spain (2 documents, 32 citations). The importance of the Swedish universities is evident from their positions in all clusters.

Discussion and Conclusions
Using the bibliometric analysis of the publications in WoS, this article shows the research trends in the economic analysis of MSW management systems, firstly from a general perspective by studying articles that analyze the economic aspects (EA), then more specifically by concentrating on those articles that present or develop a methodology for the economic analysis of these systems (MEA). The importance of this article lies in the fact that, up to now, there have been no bibliometric studies that have analyzed the economic aspects of MSW management systems. Another important point is the analysis of articles that present a methodology for analyzing the external impacts or externalities.
The bibliometric analysis shows the interest in the subjects of EA and MEA, which is evident from the increase in the number of publications. The United States, Italy, and China are the countries with the most publications in both areas. In the developing world, research into this field is scarce. Analysis of the MEA area shows that the LCC and CBA are the principal methods used to analyze the economic aspects, which were also the most representative keywords. The analysis of keywords also shows a greater emphasis on research into specific types of waste, such as "organic waste", "food waste", and "packaging waste". The importance of research into these types of waste is because they represent the most typical waste generated worldwide, along with many possible negative impacts (economic, environmental and social) caused by incorrect management.
In general, an increase can be seen in the number of publications focusing on converting waste to energy. The energy recovery of waste in incineration plants provides an opportunity to reduce the amount of waste sent to landfill. Additionally, it can help reduce the dependency on energy generated by fossil fuels, which usually have to be imported [57]. However, the rise in publications is not in line with the hierarchy of waste, as established by organizations such as the European Parliament. This hierarchy prioritizes the adoption of methods to reduce the generation of waste, increase preparations for reuse and recycling, and discourages the use of incinerators and landfills,

Discussion and Conclusions
Using the bibliometric analysis of the publications in WoS, this article shows the research trends in the economic analysis of MSW management systems, firstly from a general perspective by studying articles that analyze the economic aspects (EA), then more specifically by concentrating on those articles that present or develop a methodology for the economic analysis of these systems (MEA). The importance of this article lies in the fact that, up to now, there have been no bibliometric studies that have analyzed the economic aspects of MSW management systems. Another important point is the analysis of articles that present a methodology for analyzing the external impacts or externalities.
The bibliometric analysis shows the interest in the subjects of EA and MEA, which is evident from the increase in the number of publications. The United States, Italy, and China are the countries with the most publications in both areas. In the developing world, research into this field is scarce. Analysis of the MEA area shows that the LCC and CBA are the principal methods used to analyze the economic aspects, which were also the most representative keywords. The analysis of keywords also shows a greater emphasis on research into specific types of waste, such as "organic waste", "food waste", and "packaging waste". The importance of research into these types of waste is because they represent the most typical waste generated worldwide, along with many possible negative impacts (economic, environmental and social) caused by incorrect management.
In general, an increase can be seen in the number of publications focusing on converting waste to energy. The energy recovery of waste in incineration plants provides an opportunity to reduce the amount of waste sent to landfill. Additionally, it can help reduce the dependency on energy generated by fossil fuels, which usually have to be imported [57]. However, the rise in publications is not in line with the hierarchy of waste, as established by organizations such as the European Parliament. This hierarchy prioritizes the adoption of methods to reduce the generation of waste, increase preparations for reuse and recycling, and discourages the use of incinerators and landfills, practices which are still common in parts of Europe and elsewhere. Analysis of the waste management systems (collection and treatment) is also important as they can reduce the generation of waste and increase the potential for reuse and recycling as opposed to incineration and landfills.
The economic aspect is of great importance, as it is a fundamental part of governmental and national decision making [15], but it is also important for the possible impacts (positive or negative) of MSW management systems, on society, and the environment, to be reflected in the costs and considered by decision-makers [61]. It can also be seen how this work does not consider an economic valuation of the impacts on society, nor the possible effects on public health, of the MSW management systems. Nevertheless, the effects on public health are a very important aspect of waste, as they are associated with every stage of the handling, treatment and elimination of waste, either directly or indirectly [62]. Therefore, the impacts on public health can be decisive factors in economically evaluating a MSW system. This work can help researchers highlight different concepts and links between them, leading to further areas of research. In this case, this article reveals several trends in research. The first is the growing importance of the fields of EA and MEA, as shown by the increasing numbers of publications in the WoS. The second is the limited number of studies into developing methodologies for the economic analysis of externalities, which shows the need for more research in this field. In third place, the increasing interest in research into the use of waste to produce energy. The next emphasis is on the need for joint work by different universities (in different countries), as little collaboration has been observed. This collaboration would enable an exchange of knowledge and better management systems. Finally, more research is needed in this field from the developing countries.
Decision-makers will also find this work useful, as its results will help them to find the most economic systems and technologies, as well as the methodologies to evaluate these systems, thereby improving their decisions. Governments can develop policies, incentives, and regulations, based on the economic results of the different studies, to increase or discourage the use of certain technologies or management systems and thereby improve environmental, social or economic sustainability [63].
For the future, it is recommended that the search for articles is widened by the use of other well-known databases, such as Scopus [64]. Next, the search could be limited to a specific journal [18]. The third option would be to focus the bibliometric analysis of EA on treatment systems such as incineration, recycling and landfilling, among others. Finally, another interesting analysis would be to compare the number of results in terms of the three pillars of sustainability, the social, environmental, and/or economic areas.